Fake-finger determination device, fake-finger determination method, and fake-finger determination program

ABSTRACT

A fake finger in which a transparent thin film is attached to a finger surface is discriminated. A fake-finger determination device includes: an imaging unit  10  that captures an authentication object as a fingerprint authentication object; a classifying unit  31  that classifies an image captured by the imaging unit  10  into a plurality of regions including at least a skin region and a background region using colors of pixels included in the image; and a determining unit  32  that determines whether or not a foreign substance is present in the periphery of a finger based on a feature of a region classified as neither the skin region nor the background region out of the regions classified by the classifying unit  31.

The present invention relates to a fake-finger determination device, afake-finger determination method, and a fake-finger determinationprogram.

BACKGROUND

In recent years, fingerprint authentication has been attractingattention as one of authentication methods for identifying anindividual. Fingerprints differ person to person and have a feature thatdoes not change even though years have passed. Thus, fingerprintauthentication is considered having higher reliability than currentlyprevailing password authentication and the like. Meanwhile, infingerprint authentication, it is necessary to prevent wrongdoing thatsomeone impersonates another person using a fake finger forged usinganother person's fingerprint. As techniques for preventing suchwrongdoing, for example, Patent Documents 1 and 2 disclose techniques ofdetecting a fake finger based on a color of a surface of a fingerirradiated with light.

Patent Document 1: Patent Publication JP-A-2003-50993

Patent Document 2: Japanese Patent Publication No. 2637253

However, in Patent Documents 1 and 2, since a fake finger is detectedbased on a color of a surface of a finger, a fake finger made such thata transparent or flesh-colored thin film duplicated from anotherperson's fingerprint is attached to a surface of a finger is hardlydiscriminated. This is because, in Patent Documents 1 and 2, a fakefinger with a transparent thin film attached thereto is hardlydiscriminated since a color of a fake finger surface assimilates with acolor of a skin.

SUMMARY

The invention has been made to solve the above-mentioned problems, andit is an object of the present invention to provide a fake-fingerdetermination device, a fake-finger determination method, and afake-finger determination program, which are capable of determining afake finger in which the transparent thin film is attached to thesurface of the finger.

According to an aspect of the invention, there is provided a fake-fingerdetermination device including: an imaging unit that captures anauthentication object as a fingerprint authentication object; aclassifying unit that classifies an image captured by the imaging unitinto a plurality of regions including at least a skin region and abackground region using colors of pixels included in the image; and adetermining unit that determines whether or not a foreign substance ispresent in the periphery of a finger based on a feature of a regionclassified as neither the skin region nor the background region out ofthe regions classified by the classifying unit.

According another aspect of the invention, there is provided a method ofdetermining a fake finger, including the steps of: capturing anauthentication object as a fingerprint authentication object;classifying an image captured in the capturing step into a plurality ofregions including at least a skin region and a background region usingcolors of pixels included in the image; and determining whether or not aforeign substance is present in the periphery of a finger based on afeature of a region classified as neither the skin region nor thebackground region out of the regions classified in the classifying step.

A fake-finger determination program according to the present inventioncauses a computer to execute the steps included in the above method ofdetermining the fake finger.

According to the invention, it is possible to determine a fake finger inwhich a transparent thin film is attached to a surface of a finger.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a schematic configuration of afake-finger determination device according to each embodiment.

FIG. 2 is a schematic diagram illustrating a classifying state when afake finger in which a transparent thin film is attached to a surface ofa human finger is captured as an authentication object.

FIG. 3 is a flowchart illustrating a process procedure for determining afake finger according to a first embodiment of the invention.

FIG. 4 is a flowchart illustrating a process procedure for determining afake finger according to a second embodiment of the invention.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of a fake-finger determinationdevice, a fake-finger determination method, and a fake-fingerdetermination program according to the present invention will bedescribed.

First, how the inventors achieve the invention will be described. If aperson who desires to impersonate another person using a transparentthin film forged from another person's fingerprint at the time offingerprint authentication, the person needs to cover his/herfingerprint with the thin film. In this case, the size of the thin filmis inevitably larger than a range in which a fingerprint of a finger isscanned. Therefore, a part of the thin film is considered to protrude inthe periphery of the finger when the thin film is attached to the fingerand then the fingerprint authentication is performed.

The invention has been made by focusing on this problem and ischaracterized in that the fake finger in which a transparent thin filmis attached to a finger surface is determined by detecting the thin filmprotruding in the periphery of the finger. Hereinafter, embodiments ofthe fake-finger determination device according to the invention will bedescribed in detail on this premise.

First Embodiment

First, a schematic configuration of a fake-finger determination deviceaccording to a first embodiment will be described with reference toFIG. 1. FIG. 1 is a diagram illustrating a schematic configuration of afake-finger determination device according to each embodiment. Afake-finger determination device 1 is a device that determines whetheror not an authentication object which is a fingerprint authenticationobject is a fake finger. For example, a finger that is an authenticationobject is placed on a predetermined placement area provided on a topsurface of the fake-finger determination device 1.

As illustrated in FIG. 1, the fake-finger determination device 1includes an imaging unit 10, a light source unit 20, and a control unit30. The imaging unit 10 is, for example, a camera and captures anauthentication object placed in the installation region. The lightsource unit 20 is, for example, a light-emitting diode (LED) andirradiates the authentication object with light when the imaging unit 10captures the authentication object.

The imaging unit 10, the light source unit 20, and the control unit 30of the fake-finger determination device 1 are similar to an imagingunit, a light source unit, and a control unit of a conventionalfingerprint authentication device, respectively, in principle. However,the fingerprint authentication device of the invention is different fromthe conventional fingerprint authentication device in that the controlunit 30 has various functions for determine whether or not anauthentication object is authentic.

The fake-finger determination device 1 is physically configured toinclude a central processing unit (CPU), a memory, an imaging unit, anda light source unit. For example, the memory includes a read only memory(ROM) that stores a program or data processed by the CPU and a randomaccess memory (RAM) used as various work areas mainly for controlprocessing. The components are connected to one another via a bus. TheCPU executes the program stored in the ROM and performs processing usingdata captured by the imaging unit or data developed in the RAM, so thatfunction of the respective units of the fake-finger determination device1, which will be described later, can be implemented.

The control unit 30 controls the fake-finger determination device 1 ingeneral by executing a variety of control processes. For example, thecontrol unit 30 includes a classifying unit 31 and a determining unit32.

The classifying unit 31 classifies an image captured by the imaging unit10 into a skin region, a background region, and a remaining region usingcolors of pixels included in the image. Specifically, the classifyingunit 31 classifies the image into the skin region, the backgroundregion, and the remaining region in the following manner.

The classifying unit 31 divides the captured image into three regions byusing a color of a pixel included in the image captured by the imagingunit 10 as a feature quantity. The feature quantity used to divide theimage may include, for example, a hue value of a pixel. A technique ofdividing the image into three regions may include, for example, ak-means technique.

The classifying unit 31 computes each representative value of eachdivided region. The representative value may include, for example, anaverage of the hue values of pixels included in each region, a hue valueof a pixel most abundant in each region, or the like. The classifyingunit 31 classifies a region having a representative value closest to askin color as the skin region based on the representative value computedfor each region. Whether or not the representative value is close to theskin color may be determined, for example, based on the hue value.Specifically, the classifying unit 31 sets a region having a hue value,as a representative value, within a predetermined range that can betreated as a skin color to the skin region out of three regions. Thepredetermined range may include, for example, a range of approximately10 degrees to 50 degrees that can be treated as a flesh colorcorresponding to a skin color assuming that a red color is set to 0degree in a hue, saturation, and value (HSV) color space. In addition,if there are a plurality of regions serving as a target of the skinregion, for example, a region having a representative value closest to acenter value of the predetermined range that can be treated as a skincolor may be classified as the skin region.

The classifying unit 31 classifies a region having the representativevalue closer to the background color as the background region based onthe representative values of two regions other than the skin region.Specifically, the classifying unit 31 sets a region having a hue value,as the representative value, within a predetermined range that can betreated as a background color out of two regions other than the skinregion to the background region. In addition, in a case where both therepresentative values of two regions are within a predetermined range,for example, a region having a representative value closer to the centervalue of a predetermined range that can be treated as a background colorcan be classified as the background region. As a result, a regionclassified as neither the skin region nor the background region isclassified as the remaining region. In addition, since white turbidityor the like may occur even when transparency of the thin film attachedto the surface of the finger is high, a difference is inevitablygenerated between the background color and the color of the thin film.This allows to distinguish between the background region and the thinfilm region.

Here, detailed examples of the skin region, the background region, andthe remaining region classified by the classifying unit 31 areillustrated in FIG. 2. FIG. 2 is a diagram schematically illustrating aclassification state when the fake finger in which the transparent thinfilm is attached to the surface of the human finger as an authenticationobject is captured. The image A of FIG. 2 corresponds to a human finger,the image B corresponds to a background, and the image C corresponds toa transparent thin film. The classifying unit 31 divides the capturedimage into regions A and Ca, B, and Cb by using the colors of the pixelsincluded in the captured image of FIG. 2 as the feature quantity. Theclassifying unit 31 classifies the regions A and Ca having therepresentative value closest to the skin color as the skin region basedon the representative values of each divided region. The classifyingunit 31 classifies the region B having the representative value closerto background color as the background region. The classifying unit 31classifies the region Cb as the remaining region.

In addition, if the background color is not apparent, and it isdifficult to set in advance, the range of the hue value that can betreated as the background color, the classification may be made byconsidering a positional relation between two regions other than theskin region. Specifically, the region located further outside of theskin region may be set as the background region. In addition, even whenit is easy to set in advance, the range of the hue value that can betreated as the background color, the classification may be made byconsidering both the method of using the representative value and themethod of using the positional relation.

The determining unit 32 determines whether or not the remaining regionclassified as neither the skin region nor the background region out ofthe regions classified by the classifying unit 31 is the region obtainedby excessively dividing either the skin region or the background region.Whether or not the region is excessively divided may be determined, forexample, based on a distance or similarity between the representativevalue of the remaining region and each representative value of the skinregion or the background region.

If it is determined that the remaining region is the excessively dividedregion, it is determined that a foreign substance is not present in theperiphery of the finger, that is, the authentication object is a humanfinger. In this manner, it is determined whether or not the remainingregion is the excessively divided region, and it is determined that theauthentication object is a human finger if the remaining region is theexcessively divided region. Therefore, it is possible to prevent a casewhere a genuine human finger is erroneously determined as the fakefinger when the fair human finger is placed.

The determining unit 32 determines whether or not a foreign substance ispresent in the periphery of the finger based on the size of theremaining region if it is determined that the remaining region is notthe excessively divided region. Specifically, the determining unit 32determines that a foreign substance is present in the periphery of thefinger, that is, the authentication object is the fake finger, if thenumber of pixels of the remaining region is equal to or greater than apredetermined number. The predetermined number corresponds to, forexample, an upper limit of the number of pixels (upper limit pixelnumber) detected as a noise.

Next, a fake-finger determination process executed by the fake-fingerdetermination device according to the first embodiment will be describedwith reference to FIG. 3. FIG. 3 is a flowchart illustrating a processprocedure for determining a fake finger in which a transparent thin filmis attached to a surface of a finger.

Initially, as the authentication object is placed in the installationregion of the fake-finger determination device 1, the light source unit20 irradiates light onto the authentication object, and the imaging unit10 captures the authentication object (step S101).

Subsequently, the classifying unit 31 divides the image captured by theimaging unit 10 into three regions by using the colors of pixelsincluded in the captured image as a feature quantity (step S102).

Subsequently, the classifying unit 31 computes each representative valueof each region divided in step S102 described above (step S103).

Subsequently, the classifying unit 31 classifies the region having arepresentative value closest to a skin as the skin region based on therepresentative values of each region computed in step S103 describedabove (step S104).

Subsequently, the classifying unit 31 classifies a region having arepresentative value closest to the background as the background regionbased on the representative values of two regions other than the skinregion (step S105).

Subsequently, the determining unit 32 determines whether or not theremaining region classified as neither the skin region nor thebackground region out of three regions divided in step S102 describedabove is a region obtained by excessively dividing the skin region (stepS106). If it is determined YES in step S106, the process advances tostep S110 described below.

Otherwise, if it is determined that the remaining region is not theregion obtained by excessively dividing the skin region in step S106described above (NO in step S106), the determining unit 32 determineswhether or not the remaining region out of three regions divided in stepS102 described above is the region obtained by excessively dividing thebackground region (step S107). If it is determined YES in step S107, theprocess advances to step S110 described below.

Otherwise, if it is determined that the representative value does notcorrespond to the region obtained by excessively dividing the backgroundregion in step S107 described above (NO in step S107), the determiningunit 32 determines whether or not the number of pixels of the remainingregion out of three regions divided in step S102 described above isequal to or greater than a predetermined upper limit pixel number (stepS108). If it is determined NO in step S108, the determining unit 32determines that a foreign substance is not present in the periphery of afinger (step S110). That is, it is determined that the authenticationobject is a human finger, and the fake-finger determining process isterminated.

Otherwise, if it is determined the number of pixels in the remainingregion is equal to or greater than a predetermined upper limit pixelnumber in step S108 (YES in step S108), the determining unit 32determines that a foreign substance is present in the periphery of afinger (step S109). That is, it is determined that the authenticationobject is the fake finger, and the fake-finger determining process isterminated.

As described above, in the fake-finger determination device 1 accordingto the first embodiment, the image captured by the imaging unit 10 canbe classified into the skin region, the background region, and theremaining region. In addition, if the number of pixels in the remainingregion is equal to or greater than a predetermined number, it can bedetermined that a foreign substance is present in the periphery of afinger. As a result, it is possible to detect the thin film portionprotruding in the periphery of a finger even when the fake finger inwhich the transparent thin film is attached to the surface of the fingeris used. Therefore, it is possible to improve determination accuracy ofthe fake finger.

In the fake-finger determination device 1 according to the firstembodiment, it is determined whether or not the remaining region is theregion obtained by excessively dividing the skin region or thebackground region. If it is determined that the remaining region is theexcessively divided region, it is possible to determine that thefingerprint corresponds to a human finger. As a result, it is possibleto prevent a case where a genuine human finger is erroneously determinedas the fake finger when the fair human finger is placed.

Second Embodiment

The second embodiment of the invention will be described. A fake-fingerdetermination device according to the second embodiment is differentfrom the fake-finger determination device according to the firstembodiment described above in the function of a classifying unit 31 of acontrol unit 30. Other configurations are similar to those of thefake-finger determination device according to the first embodiment.Therefore, like reference numerals denote like elements, and descriptionthereof will not be repeated. The following description will focus on adifference between the first and second embodiments.

The classifying unit 31 according to the second embodiment is similar tothe classifying unit 31 according to the first embodiment in that theimage captured by an imaging unit 10 is classified into the skin region,the background region, and the remaining region using the colors of thepixels included in this image. However, a specific method of classifyingthe image into the skin region, the background region, and the remainingregion is different. Hereinafter, how the classifying unit 31 classifiesthe image into the skin region, the background region, and the remainingregion according to the second embodiment will be described in detail.

The classifying unit 31 classifies, as the skin region, a group ofpixels having a color that can be treated as a skin out of each pixelincluded in the image captured by the imaging unit 10. The color thatcan be treated as a skin may include, for example, a hue value that canbe treated as a skin. The hue value that can be treated as a skincorresponds to approximately 10 degrees to 50 degrees that can betreated as a hue value of a skin color assuming the hue value of a redcolor is set to 0 degree in the HSV color space.

The classifying unit 31 classifies, as the background region, a group ofpixels having a color that can be treated as the background out of eachpixel included in the image captured by the imaging unit 10. The colorthat can be treated as the background may include, for example, a huevalue that can be treated as the background. As a result, a group ofpixels classified as neither the skin region nor the background regionare classified as the remaining region.

If the background color is not apparent, a portion corresponding to theskin region out of the image captured by the imaging unit 10 is dividedinto two regions by using the colors of pixels included in this portionas the feature quantity, and the region located in an outer side can beclassified as the background region based on the positional relationbetween two divided regions. The feature quantity used in the dividingmay include, for example, a hue value of the pixel. The method ofdividing the image into two regions may include, for example, a k-meanstechnique.

Next, a fake-finger determining process executed by the fake-fingerdetermination device according to the second embodiment will bedescribed with reference to FIG. 4. FIG. 4 is a flowchart illustrating aprocess procedure for determining the fake finger in which a transparentthin film is attached to the finger surface. Since steps S201 and S204to S208 illustrated in FIG. 4 are similar to steps S101 and S106 to S110of FIG. 3, they will not be repeatedly described. Here, the followingdescription will focus on the processing details of steps S202 and S203different from those of FIG. 3.

As shown in FIG. 4, when the authentication object is captured in stepS201, the classifying unit 31 classifies, as the skin region, a group ofpixels having a color that can be treated as a skin out of each pixelincluded in the image captured by the imaging unit 10 (step S202).

Subsequently, the classifying unit 31 classifies, as the backgroundregion, a group of pixels having a color that can be treated as abackground out of each pixel included in the image captured by theimaging unit 10 (step S203).

Then, similar to the first embodiment described above, the determiningunit 32 determines whether or not the remaining region classified asneither the skin region nor the background region is the region obtainedby excessively dividing the skin region or the background region (stepsS204 and S205) and whether or not the number of pixels in the remainingregion is equal to or greater than a predetermined upper limit pixelnumber (step S206).

As described above, in the fake-finger determination device 1 accordingto the second embodiment, it is possible to classify the image capturedby the imaging unit 10 into the skin region, the background region, andthe remaining region. Then, if the number of pixels in the remainingregion is equal to or greater than a predetermined number, it ispossible to determine that a foreign substance is present in theperiphery of the finger. As a result, even in the fake finger in whichthe transparent thin film is attached to the surface of the finger, itis possible to detect the thin film portion protruding in the peripheryof the finger. Therefore, it is possible to improve determinationaccuracy of the fake finger.

In the fake-finger determination device 1 according to the secondembodiment, it is determined whether or not the remaining region is theregion obtained by excessively dividing the skin region or thebackground region. If it is determined that the remaining region is theexcessively divided region, it is determined that the image correspondsto the human finger. As a result, it is possible to prevent a case wherea finger of a genuine human is erroneously determined as a fake fingerwhen the finger of the legitimate human is placed.

Embodiments described above are just exemplary and may encompass variousmodifications or technical applications although they are notspecifically provided in the description of the embodiments. That is,the invention may be modified in various other forms without departingfrom the spirit or scope of the invention.

For example, although the image captured by the imaging unit 10 isclassified into three regions including the skin region, the backgroundregion, and the remaining region according to the embodiments describedabove, the number of the classified regions is not limited to three. Theimage may be classified into a plurality of regions including at leastthe skin region and the background region.

Although it is assumed that the capturing range of the imaging unit 10is larger than the authentication object, and a background is present inthe periphery of the authentication object in the embodiments describedabove, such an assumption may not be satisfied. For example, if thecapturing range of the imaging unit is small, the background or the filmis not likely to appear in the captured image. If the background or thefilm does not appear in the captured image, it is impossible to identifythe fake finger using the invention. Accordingly, it is preferable touse the present invention when the background appears in the capturedimage, and not to use the present invention when the background does notappear in the captured image. In order to implement such aconfiguration, for example, the following process may be furtherincluded in the fake-finger determination process described above.

If the ratio of a skin region with respect to the entire image capturedby the imaging unit 10 is smaller than a predetermined value, thedetermining unit 32 determines that a background is present and thendetermines whether or not a foreign substance is present in theperiphery of a finger. Meanwhile, if the ratio of the skin region withrespect to the entire image captured by the imaging unit 10 is equal toor greater than the predetermined value, the determining unit 32determines that a background is not present and skips the fake-fingerdetermination process without determining whether or not a foreignsubstance is present in the periphery of a finger.

The predetermined ratio may be set to, for example, a lower limit of theratio when it is assumed that a background is not present. Through theprocess described above, the necessity of providing the imaging unithaving a capturing range larger than the authentication object may beavoided.

Although the determining unit 32 according to the embodiments describedabove determines whether or not a foreign substance is present in theperiphery of a finger based on the size of the remaining region, thecriterion for determination is not limited to the size of the region.For example, it is possible to determine whether or not a foreignsubstance is present in the periphery of a finger based on such featureof the remaining region as a shape or position of the remaining region.

This application is based on and claims the priority of Japanese PatentApplication No. 2009-256971 filed Nov. 10, 2009, hereby incorporated byreference as set forth fully herein.

While exemplary embodiments of the invention have been described andillustrated hereinbefore, they are not intended to limit the scope ofthe invention. They may be variously modified or changed withoutdeparting from the spirit or scope of the invention as appreciable bythose skilled in the art.

The fake-finger determination device, the fake-finger determinationmethod, and the fake-finger determination program according to theinvention are suitably applied to determination of a fake finger inwhich a transparent thin film is attached to the finger surface.

1 fake-finger determination device

10 imaging unit

20 light source unit

30 control unit

31 classifying unit

32 determining unit

1. A fake-finger determination device comprising: an imaging unit thatcaptures an authentication object as a fingerprint authenticationobject; a classifying unit that classifies an image captured by theimaging unit into a plurality of regions including at least a skinregion and a background region using colors of pixels included in theimage; and a determining unit that determines whether or not a foreignsubstance is present in the periphery of a finger based on a feature ofa region classified as neither the skin region nor the background regionout of the regions classified by the classifying unit.
 2. Thefake-finger determination device according to claim 1, wherein thedetermining unit determines that a foreign substance is present in theperiphery of a finger based on a size of the region classified asneither the skin region nor the background region.
 3. The fake-fingerdetermination device according to claim 1, wherein the classifying unitdivides the image captured by the imaging unit into three regions usingcolors of pixels included in the image, and classifies a region having afeature quantity closest to a skin color as the skin region based onfeature quantities of colors in the three divided regions.
 4. Thefake-finger determination device according to claim 3, wherein theclassifying unit classifies a region having a feature quantity closer toa color of a background as the background region based on featurequantities of colors in two regions other than the region classified asthe skin region.
 5. The fake-finger determination device according toclaim 3, wherein the classifying unit classifies, as the backgroundregion, a region located further outside of the skin region out of tworegions other than the region classified as the skin region.
 6. Thefake-finger determination device according to claim 1, wherein theclassifying unit classifies, as the skin region, a pixel having a colorthat can be treated as a skin out of pixels included in the imagecaptured by the imaging unit.
 7. The fake-finger determination deviceaccording to claim 6, wherein the classifying unit classifies, as thebackground region, a pixel having a color that can be treated as abackground out of pixels included in the image captured by the imagingunit.
 8. The fake-finger determination device according to claim 6,wherein the classifying unit divides a portion not included in the skinregion out of the image captured by the imaging unit into two regionsusing colors of pixels included in the portion and classifies, as thebackground region, a region located further outside of the skin regionout of the two divided regions.
 9. The fake-finger determination deviceaccording to claim 1, wherein the determining unit determines whether ornot a region classified as neither the skin region nor the backgroundregion out of the regions classified by the classifying unit is a regionobtained by excessively dividing either the skin region or thebackground region, and determines whether or not a foreign substance ispresent in the periphery of a finger if it is determined that the regionclassified as neither the skin region nor the background region is notthe excessively divided region.
 10. The fake-finger determination deviceaccording to claim 1, wherein the determining unit determines whether ornot a foreign substance is present in the periphery of a finger if aratio of the skin region with respect to the entire image captured bythe imaging unit is smaller than a predetermined ratio when it isassumed that a background is not present.
 11. A method of determining afake finger, comprising the steps of: capturing an authentication objectas a fingerprint authentication object; classifying an image captured inthe capturing step into a plurality of regions including at least a skinregion and a background region using colors of pixels included in theimage; and determining whether or not a foreign substance is present inthe periphery of a finger based on a feature of a region classified asneither the skin region nor the background region out of the regionsclassified in the classifying step.
 12. A fake-finger determinationprogram causing a computer to execute the steps recited in claim 11.